There I made an interesting discovery about the whirlwheel toy. You can pick it up with a stick if your dog won't bring it back on land. Penny always waits just in the water, ready for the second toy to be thrown. She won't put down the first until she is quite sure there's another one in flight.
Here's my patented method for picking up this toy:
And here's Penny hanging on to the first one, watching, watching, watching for the throw of the second toy: